A study on an optical imaging device which radiates light on a biological body from a light source such as a laser and converts information about an interior of the biological body obtained based on incident light into an image is actively advanced in a medical field. As one of optical imaging techniques, there is a photoacoustic tomography (PAT). The photoacoustic tomography refers to a technique of radiating pulsed light, produced from a light source, on a biological body, and detecting and analyzing an acoustic wave (typically, ultrasound) produced by biological tissues which absorbed energy of pulsed light having propagated and diffused in the biological body to visualize intra-subject information. More specifically, by utilizing the difference in the absorptance of optical energy between a subject site such as a tumor and tissues other than the subject site, an acoustic detector (referred to as “probe” or “transducer”) receives an elastic wave which is produced when the subject site absorbs optical energy radiated on the subject site and instantaneously expands. By mathematically analyzing this detected signal, an initial acoustic pressure distribution or an optical characteristic distribution in the biological body, particularly, an absorption coefficient distribution, can be obtained. These pieces of information can be also utilized to quantitatively measure specific substances in the subject such as a hemoglobin concentration included in blood or oxygen saturation in blood by using lights of various wavelengths. In recent years, using this photoacoustic tomography, a pre-clinical study of imaging blood vessel images of small animals or clinical study of applying this principle to diagnosis of, for example, breast cancer, are actively advanced (NPL 1).
In an acoustic wave probe which is usually used in a photoacoustic tomography device, a frequency of an acoustic wave to be detected is limited (band limitation). Hence, there is a problem that an image to be obtained may deteriorate when a normal image reconstruction method which assumes the ideal acoustic wave probe characteristics is used. In response to this problem, a method is proposed for decreasing the influence of a probe on image deterioration, by measuring in advance an impulse response of an acoustic wave probe (response characteristic data unique to an element) and correcting (for example, deconvoluting) the detection signal according to this impulse response (NPL 2).